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Configuration:

CPU: Intel Core i7-4790K

Motherboard: ASUS Z97-A ATX DDR3 2600 LGA 1150

RAM: Crucial Ballistix Sport XT 16GB Kit (8GBx2) DDR3 1866

PSU: Corsair RM750

When I turn the PC on, the CPU fan turns on for about one second. Also, the EZ XMP LED(XLED1) turns green for a second. This happens about every 3 seconds until I turn off the PSU.

I disconnected all the drives and GPU, but that didn't change anything.

The only time when the CPU fan turns continuously is when I unplug the 8-pin CPU connector from PSU, so that only the the 24-pin MOBO connector is plugged in.

Trying to fix this, I got a new PSU (same model), but that didn't help.

Sorry if I missed any details. I will be happy to provide them.

Any suggestions on how to troubleshoot this?

Update: Sorry, I forgot to mention in the original post that I had cleared CMOS a couple of times. That didn't help.

Update 2: Again, sorry I didn't explicitly mention in the original post that all the USB devices (keyboard and the mouse) had been unplugged for troubleshooting.

Update 3: Got another motherboard. Installed the CPU. It works. So, it looks like the motherboard was at fault. Now the PC won't recognize the old Windows system disk, but that's another story :)

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  • 1
    The first thing I would try is clearing the CMOS. Your motherboard isn't very happy about something.
    – Mr Ethernet
    Commented Aug 8, 2019 at 22:00
  • Sounds like a motherboard or cpu failure.
    – Moab
    Commented Aug 8, 2019 at 22:17
  • Im going to be a little nit-picky, but your title triggers me a little. Just because your PC worked for 4 years doesnt have any bearing on whether or not it will work now.
    – Keltari
    Commented Aug 9, 2019 at 19:30
  • 1
    @Keltari Many people have similar questions about new builds. I wanted to stress that this is a valid hardware configuration.
    – user1566515
    Commented Aug 9, 2019 at 19:47
  • @user1566515 Im not sure what you mean by "valid." Either it works, or it doesnt. If something stops working, something broke, which doesnt make it any less "valid."
    – Keltari
    Commented Aug 9, 2019 at 20:25

2 Answers 2

Reset to default
2

The motherboard has suffered a catastrophic failure.

This was always the most likely possibility. The description of the CPU fan as rhythmically starting and stopping by itself almost always points to a failed motherboard (or one that needs a CMOS reset, which has already been ruled out.)

The failure rate for motherboards compared to CPUs is also vastly higher in general. I have had to replace over a dozen motherboards but have yet to come across a single CPU failure. CPU failures are rare as they have fewer potential points of failure than motherboards and almost always outlive them.

In terms of proof that it's the motherboard and not the CPU, the ASUS Z-97 manual actually describes how a failed CPU can easily be recognized by the illumination of a dedicated CPU POST-failure LED on the motherboard itself.

The manual also describes how if the motherboard does find an error with either the CPU, boot device, DRAM or VGA module, it will not reboot itself as is happening in this situation, but will simply keep the corresponding POST-failure LED steadily lit until the error is resolved. That's not what's happening here: it's continually restarting itself.

Everything points to a bad motherboard.

enter image description here

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15
  • Thank you! This makes a lot of sense. Do you think it's also possible that both the motherboard and the CPU have failed?
    – user1566515
    Commented Aug 9, 2019 at 13:35
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    @CliffArmstrong oh I'm sure the OP has already tried disconnecting all USB and other peripherals and got his system down to its core components by this stage of the troubleshooting process.
    – Mr Ethernet
    Commented Aug 9, 2019 at 22:23
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    @CliffArmstrong after the OP confirms that disconnecting all USB devices and other peripherals makes no difference whatsoever, please feel free to remove your downvote. It's odd that you're downvoting the correct answer but didn't downvote the other answer, that went off in the completely wrong direction (recommended buying a PSU tester!)
    – Mr Ethernet
    Commented Aug 9, 2019 at 22:53
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    Sorry I didn't explicitly mention in the original post that all the USB devices (keyboard and the mouse) had been unplugged. The devices mentioned in the "Configuration" part (plus a monitor via HDMI) are the only "players" in my test.
    – user1566515
    Commented Aug 11, 2019 at 21:14
  • 2
    Yes, it was the motherboard. Thanks again!
    – user1566515
    Commented Aug 14, 2019 at 3:16
-1

ATX Power supply tester

can find mail order < $20

  • step1: u already did, disconnect everything & have just power supply and motherboard
    • if onboard video and looks like it's booting but nothing on screen then scrounge a working graphics card
    • if no onboard video, then try a second known working graphics card to rule out graphics card
    • goal is simply pass Power On Self Test and get the bios/efi screen to show on monitor
  • step2: if it's obvious that it's not making it that far, then it's narrowed down to either PSU or mobo
    • can try an ATX psu power tester, or try another known good working psu; goal again passing POST assuming mobo is good
    • if PSU checks out then assume mobo bad; if there are blinking led's representing an error code then track that down { for example some Dell's typically blink the power button led in a certain sequence to represent some error}

clearing CMOS via the mobo jumper is also a not a bad idea to try since it's easy to do... maybe make this step 1.5

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1
  • I tried 2 PSUs, one of them brand new. It's pretty clear at this point that the problem is with CPU and/or mobo. The question is how to narrow it down. I don't know if it's possible without having spare CPU or mobo laying around.
    – user1566515
    Commented Aug 9, 2019 at 1:19

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